In recent years, an increasing number of vehicles mount a camera to allow the driver of the vehicle to visually recognize a view laterally or rearwardly, etc. of the vehicle through a monitor unit mounted inside the vehicle. Further, there has been developed an apparatus for assisting a driving operation such as an operation for parking by effecting e.g. an image processing with utilization of a photographic image obtained by this camera. For the camera employed for obtaining photographic image as the basis for calculation of information such as positioning of the vehicle effected in such apparatus, particularly high precision in optical axis alignment is required. Such high optical axis alignment precision cannot be easily obtained at the time of the mounting of the camera and the high precision can be realized only through calibration of its optical axis with high precision after the mounting of the camera. As a technique for use in such calibration, one is known from Patent Document 1 identified below.
With a calibration apparatus for onboard camera described in Patent Document 1, within a field of view of the onboard camera, there is disposed a marker (a calibration index) having a black-and-white checkered pattern and a photographic image obtained by photographing this maker is subject to an image recognition operation for detection of a center point (calibration point) of the marker. This calibration apparatus effects calibration of an onboard camera with using the detected center point of the marker. This marker is provided with a colored checkered pattern and from an edge included in the photographic image obtained by the onboard camera, the calibration point formed by the checkered pattern is specified and this calibration point is used for effecting calibration of the onboard camera.